The present invention relates generally to catheter electrodes and more specifically to a catheter electrode for use in stimulating the spinal cord.
In recent years the application of the spinal cord stimulation has shown a great deal of promise in the treatment of pain and various motor disorders. Initially the leads were implanted in the cervical area by a small laminectomy and applied to the dura in the epidural space along the midline under direct vision. This requires an operation in the cervical area where two or three spinous processes and one set of lamina are removed.
The next generation of stimulation electrodes were positioned by percutaneous implantation. This procedure could be carried out under a local anesthetic. The electrodes were passed into the epidural space while being monitored by flouroscopy until they were placed at the desired level. Unfortunately, the only electrodes that were presently available were single electrodes. Thus, it was necessary to make two separate puncture wounds and position two independent electrodes along the midline of the spinal cord. A description of the prior art devices and the improvement thereto is described in U.S. Pat. No. 4,044,774.
Due to the particularities in the construction of the electrodes illustrated in the aforementioned patent, it was not possible to produce a multi-electrode catheter. The main reason for this difficulty was that the conductors connecting the contacts to the leads used a wire coiled in a helix construction. To manufacture a multi-electrode assembly would have necessitated a special insulation and manufacturing process to accommodate additional coiled conductors in the same sheath and would possibly unduly increase the diameter of the sheath.
Other problems with prior art percutaneous implanted electrodes included broken wires, displaced electrodes and the general inability to achieve satisfactory, consistent, in-line placement. The placement factor became more critical in view of recent studies that polarity plays a major role in the effectiveness of the stimulation. Thus the trend has been back to placing the electrodes in position via a laminectomy.
Multiple electrode catheters have been used in the prior art and have been directed specifically to the stimulation of the heart muscle. Typical patents are U.S. Pat. Nos. 3,348,548; 3,825,015; and 3,995,623. The spacing of the electrodes and design vary with the portions of the heart to which they desire to stimulate.
The prior art has failed to direct its efforts for providing a multiple electrode catheter which can be percutaneously inserted for spinal cord stimulation.
Catheter electrodes now being manufactured for cardiac pacing are not suitable for spinal cord stimulation since their strength is questionable under stresses imposed by placement in the spinal column. The diameter of most cardiac leads are also larger than those desirable for use in the spinal column.